1. Field of the Invention
The present invention relates to a sewing machine with a dust removing device. More particularly, the invention relates to a sewing machine with a dust removing device which is so constructed as to prevent trouble such as faulty sewing to be caused when dust including waste thread and waste cloth is collected under a throat plate, in performing, for example, interlock stitch sewing by an overlock sewing machine.
2. Description of the Prior Art
In the event that dust including waste thread and waste cloth to be produced-during sewing operation by a sewing machine, is collected at the underside of a throat plate at which sewing parts such as a looper, fabric feed mechanism and knife driving mechanism are disposed, there is a tendency that a needle thread loop is not formed in a predetermined manner, resulting in a faulty sewing such as skip-stitch. If dust is more collected there, the dust will interfere with movable parts such as a needle and looper, and thus cause the deformation and damage on the movable parts.
In order to prevent the faulty sewing and deformation of the movable parts because of the collected dust as described, the following conventional manner has generally been taken. That is, an air gun is manually operated to spray airflow around the underside of the throat plate, thereby to scatter and remove the collected dust. With this manner, however, it is sometimes required to spray airflow by interrupting the operation of the sewing machine in the course of sewing. That is, not only such a time-consuming and tedious cleaning operation but also a lot of time for this cleaning is required, resulting in a low sewing efficiency. In addition, when airflow is sprayed, the collected dust may scatter and suspend around the sewing machine, thus deteriorating working environment.
To solve these problems, U.S. Pat. No. 5,454,338 discloses a sewing machine equipped with a dust removing device (hereinafter referred to as prior art. This prior art is provided with a fan by which an external air is forced to pass through the radiator of an oil cooler for cooling lubricating oil used for lubricating the interior of the sewing machine. By introducing the airflow caused by the fan and then passed through the radiator, into the inside of the sewing machine, the interior of the sewing machine is retained at positive pressure so as to prevent dust including Waste thread, etc. from entering the sewing machine.
In this prior art so constructed, the function of preventing dust entering the sewing machine can be attained by utilizing the airflow generated by the fan for the oil cooler that is originally equipped with the sewing machine in order to cool lubricating oil. Therefore, as compared to the above-mentioned manual removing means of spraying airflow by the air gun, there is no need to perform such cleaning that is tedious and lowers sewing efficiency. That is, such a self-cleaning operation enables to prevent trouble such as faulty sewing due to the dust collected beneath the throat plate.
However, this prior art is constructed so as to merely prevent dust entering the sewing machine by introducing the above-mentioned airflow to retain its inside at positive pressure. It is therefore impossible to prevent trouble caused by the dust collected beneath the throat plate. Further, the interior of the sewing machine is not a completely closed room, and it is thus unavoidable to make working environment not hygienic. This is because, for example, the introduced airflow is blown out to the exterior from the clearance in a needle location of the throat plate, and dust is scattered and suspended around the throat plate. Furthermore, one which is introduced into the sewing machine is airflow heated by heat exchange with the radiator, and it is suppressed that the heated airflow is blown out to the exterior. Therefore, the temperature in the sewing machine will be gradually increased, thereby to facilitate a temperature rise in the movable parts such as the needle and looper which are likely to be heated by the friction during sewing operation. As a result, the thread in contact with the needle and looper is unexpectively cut by heat.